1. Field of the Invention
This invention relates to a method for preparing a liquid jet recording head to be mounted on a liquid jet recording device which performs recording by discharging liquid by utilizing heat energy to form discharged droplets and attaching the droplets onto a recording medium such as paper, etc.
Also, the present invention relates to a liquid jet recording head prepared according to the above preparation method.
Further, the present invention relates to a liquid jet recording device having the liquid jet recording head prepared according to the above preparation method mounted thereon
2. Related Background Art
Liquid jet recording method is a recording method which performs recording by forming discharged droplets of a recording liquid such as ink, etc. according to various system, and attaching the droplets to a recording medium such as paper, etc.
Among recording devices to which such recording method is applied as the device having a structure suitable for high density multi-openings, a liquid jet recording device of the type utilizing heat energy for discharged droplet formation can be included.
The liquid jet recording device utilizing heat energy as the droplet discharging energy generally has a liquid jet recording head having a droplet forming means and a liquid heating means for forming droplets of a recording liquid. The above droplet forming means has discharging openings for discharging droplets and liquid channels, including portions imparting heat to the recording liquid, and the above liquid heating means includes an electro-thermal energy convertor comprising a heat-generating resistor capable of heating the recording liquid (hereinafter called heater) and a pair of electrodes for applying electical signals to the heat-generating resistor.
The droplet forming means forms droplets of a recording liquid by applying predetermined recording signals from the electrodes to heater to generate heat from the heater, heating the recording liquid by the heat generated and creating a pressure displacement, accompanied with the volume increase caused by the abrupt foaming of the recording liquid, thereby discharging the recording liquid through the droplet discharging openings.
On the other hand, as the recording liquid to be used during recording by a liquid jet recording device, an aqueous recording liquid has been primarily used in aspects such as recording characteristics, stability in discharging, etc.
Such aqueous recording liquid is formed generally of a recording agent component such as pigment, dye, etc. and a solvent component composed primarily of water or water and a water-soluble organic solvent for dissolving or dispersing the recording agent.
In this connection, the heating limit temperature for effecting abrupt gasification of the recording liquid containing the solvent component comprising water and a water-soluble organic solvent, namely the temperature at which evaporation at the liquid-gas interface by the heat content transmitted by thermal conduction through a very thin and stable vapor membrane between the heat transmitting surface and the liquid, is 250.degree. C. to 350.degree. C.
Accordingly, for performing recording by foaming and discharging the recording liquid by applying electrical signals to the heater by use of a recording liquid having such temperature characteristics, the heater will generate heat repeatedly from normal temperature to 300.degree. to 800.degree. C. every time when electrical signals are applied.
The heater may be formed by laminating a wiring portion comprising a metal which is a good electroconductor (electrode such as Al, Au, Ag, Cu, etc.) through an intermediate layer (Ti, Cr, etc.) on a heat-generating resistor (e.g. heat resistant resistance material such as HfB.sub.2, ZrB.sub.2, TaN.sub.2, TaSi, etc.) provided on a substrate (e.g. Si, glass, ceramics, etc.) so that the intermediate layer may be exposed. Thus, the portion of the intermediate layer exposed becomes the heater.
Further, if necessary, a protective layer excellent in heat resistance, ink shielding characteristic (e.g. SiO.sub.2, Al.sub.2 O.sub.3, Si.sub.3 N.sub.4, etc.) is provided on at least the heater and the electrodes for preventing electrocorrosion, oxidation caused by the recording liquid, whereby recording liquid is shielded from these.
In the recording device with the constitution which performs droplet discharging by heating the recording liquid through repeated heat generation to high temperature from the heater with the constitution as described above with the electrical signals corresponding to the recording signals, for the purpose of improving recording characteristics (particularly characteristics of recording liquid, for example, viscosity, etc.) during recording, there have been practiced in the prior art the preliminary discharging treatments as disclosed in U.S. Pat. No. 4,712,172 and G.B. Patent Nos. 2159465, 2169856 and 2169856 or the preliminary heating treatments as disclosed in U.S. Pat. Nos. 4,463,359, 4,296,421 4,719,472 and 4,712,172, and G.B. Patent Nos. 2169855 and No. 2169856 as included in the recording mode after the liquid recording device is sold under the state where the liquid jet recording head is mounted on the above device.
By performing such treatment as described above, primarily the characteristics of the recording liquid may be improved during recording, but it may not be necessarily satisfactory as the method for accomplishing the best recording state, particularly from the initial stage.
Thus, by repeated high temperature heat generation of the heater material in the recording mode including the preliminary discharging treatment and the preliminary heating treatment as described above, phase change, stress change, oxidation and composition change may be sometimes caused to occur, whereby the resistance value of the heater material was liable to be changed gradually.
Also, changes will occur in the resistance distribution of the heater material by the interface resistance in the boundary region between the heater material and the wiring portion (electrodes), and further by the diffusion phenomenon between the above-mentioned members, etc.
If the change in heater resistance value is thus generated, the heat energy generated from the electrical signals initially set will be increased or decreased corresponding to the resistance change and will deviate from the desired value. As the result, the droplet discharging rate and its discharging amount will become gradually different from those initially set.
And, finally, when these exceed the preferable ranges for discharging of the recording liquid, deterioration in quality of recorded images to be formed by discharging of the recording liquid will be brought about.
Further, when the resistance value tends to be reduced, the heat energy generated by the heater is increased, and the heater generates more heat than the set value, whereby the heater life will be significantly reduced due to such problems as cavitation, heat resistance of the heater material, etc.
Accordingly, there have been investigated the methods in which such change in heater resistance value can be maintained within the range which will not cause defective printing and durability deterioration of the heater material.
As one method, for example, in preparation of the liquid jet recording device, there may be included the method in which the resistance value change of the heater is made smaller by applying heat treatment on the whole recording head during completion of the recording head.
Whereas, when the treatment according to such preparation method is applied, even the portion where no heating treatment other than heater is required will be heated. Accordingly, inconveniences due to heating will frequently occur at the portion where no heating is necessary. More specifically, due to the increase in internal stress of the recording head by the heating treatment, there have been generated problems such as generation of cracks or defects, warping of the recording head itself, poor adhesion on account of peel-off between the constituent members of the recording head, etc.
Further, there also occurred such problems as poor electrical resistance or contact due to oxidation of the bonding portion on account of electrical connection of the recording head to its external device, or deterioration in adhesion at their portions, etc.
Further, for obtaining the stabilizing effect of the resistance value of the heater in this method, the heating temperature is required to be made as high as 500.degree. C. or higher, whereby the materials available for the recording head constituent members are restricted to result in increased preparation cost.